Refrigeration cycle

ABSTRACT

A refrigeration system is described in two preferred embodiments. In both embodiments, the refrigeration cycle includes a conventional compressor, condenser, expansion valve and evaporator. The receiver is not in the loop normally. In one embodiment, a pressure differential valve diverts subcooled refrigerant to the receiver only in response to a predetermined difference in pressure between the saturation pressure caused by the ambient surrounding the condenser, plus spring pressure and the pressure within the line leaving the condenser. Refrigerant thus diverted is metered back into the suction side of the system. In a second embodiment, compressed gas exiting the compressor is diverted to the receiver responsive to a pressure differential between saturation pressure caused by condenser ambient plus spring pressure and the pressure within the receiver. The refrigerant thus diverted raises the pressure within the receiver which in turn drives liquid refrigerant back into the liquid line.

FIELD OF THE INVENTION

This invention relates to an improvement in refrigeration, and typicallyin commercial refrigeration units that have the standard condenser,receiver, expansion valve, and one or more compressors.

BACKGROUND OF THE INVENTION

In commercial refrigeration units, a condenser is normally located onthe roof top where heat can be exhausted to the ambient atmosphere. Theoutput from the condenser then flows to a receiver tank where it isstored and liquid from the receiver tank then flows to expansion valvesand an evaporator where cooling occurs as the refrigerant changes phasefrom liquid to gas. The output from the evaporator then travels bysuction to one or more compressors and the output from the compressorthen returns to the condenser wherein heat is extracted therefrom andthe cycle is repeated.

It is desirable to maximize the subcooling in the condenser so that therefrigerant is cooled below the phase change transition temperature andthat subcooling retained to a maximum extent as the liquid recirculates.

It is further desirable to minimize the amount of refrigerant charged tothe system and to operate at the lowest possible discharge pressure fromthe condenser.

However, when the subcooled liquid from the condenser is stored in areceiver, it may be heated. Accordingly, in U.S. Pat. No. 4,831,835, itwas proposed to bypass the receiver selectively based upon the outputtemperature of the condensed liquid from the condenser. When the liquidtemperature drops below a predetermined value indicating the desiredlevel of subcooling, the bypass is activated and the subcooledrefrigerant flows from the condenser to the expansion valves. When theliquid temperature increases above the desired level, the bypass isclosed and flow from the condenser to the receiver is opened. Accordingto the first condition the receiver remains in the flow path through apressure regulating valve even when bypassed.

SUMMARY OF THE INVENTION

It has been discovered, however, that the receiver can be effectivelyremoved from the flow path and the subcooling maximized while minimizingthe refrigerant charge by the use of dynamic regulating valves. Thevalves use a temperature sensor or power element which is disposedwithin the air stream beneath the condenser, sheltered from sun exposureto produce a signal proportional to the saturation pressure caused bythe condenser ambient. A second sensor is disposed in the liquid lineupstream of the valve. The valve then registers a differential pressurewhich in turn controls bypass flow to the receiver. This valve willhereafter be called ambient compensated pressure regulating valve. Thevalves, of course, are biased and the spring pressure also affects thesignal in the conventional manner.

In addition, although the receiver is disposed outside the flow path, ametering device can be provided to return refrigerant therefrom to thesystem when necessary. In this way, when the requirement for refrigerantis at a maximum, the refrigerant in the receiver remains active withinthe recirculating system rather than being stored in the receiver. Thisamounts to a significant reduction in refrigerant charge required tosatisfy the system during maximum demand.

In an alternative method, another ambient compensated pressureregulating valve is used to regulate the application of compressordischarge pressure to the receiver. This differential can then be usedto drive excess liquid in the receiver back into the liquid line tomaintain equilibrium of the quantity of liquid refrigerant circulatingin the system.

Accordingly, it is an object of this invention to provide arefrigeration cycle wherein the receiver tank is substantially removedfrom the flow path depending upon the differential pressure between theliquid line and the saturation pressure based on the ambient temperatureat the condenser and valve setting, (spring pressure) or similardifferential pressure or temperature to drive a control valve to achievethe described purpose.

It is another object of this invention to provide a refrigeration cycleminimizing the storage of refrigerant in the receiver whereby duringmaximum demand, liquid from the receiver is bled into the low pressureside of the system.

It is a further object of this invention to provide a refrigerationcycle wherein efficiency is maximized and the refrigerant chargeminimized based upon the differential between the saturation pressurecaused by the condenser ambient plus spring pressure and the internalline pressure.

These and other objects will become readily apparent with reference tothe drawings and following description wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a preferred refrigeration system of thisinvention.

FIG. 2 is a schematic of an alternate preferred refrigeration system ofthis invention.

DETAILED DESCRIPTION OF THE INVENTION

With attention to the drawings and to FIG. 1 in particular, the basiccomponents of the system of this invention include the conventionalelements of a refrigeration cycle, i.e., a compressor 10, a condenser12, a receiver 14 and one or more expansion valve (not shown) and anevaporator (not shown). It will be understood that the compressor 10 maybe in fact one or more of such units in parallel. The inventionhereinafter described is not dependent upon the number or size of thecompressors and in fact they may be of unequal size.

Typically, the remote condenser 12 will be situated on a rooftop and astream of air passing therethrough provides subcooling of therefrigerant circulating therethrough by natural ambient means. A powerelement or sensor 16 is provided in that air stream, sheltered from thesunlight. This sensor will reflect saturation pressure caused by thecondenser ambient.

Contrary to conventional design, the receiver 14 is not in thecirculation path for refrigerant circulating from the condenser 12through expansion valves and the evaporator and compressor to return tothe condenser. An ambient compensated pressure regulating valve 18 isprovided in the line 20 controlling the flow from the output line 22 ofthe compressor to the receiver 14. Valve 18 uses a second sensor 24upstream to measure the line pressure in line 22. Therefore, the valve18 being an ambient compensated pressure regulating valve, compares thesaturation pressure due to condenser ambient with the line pressureinternal to the output from the condenser.

When the pressure in line 22 tends to rise, as in the summertime, itwill tend to overcome the saturated pressure and valve 18 will begin toopen. Excess refrigerant may thus be diverted to the receiver to beavailable to be returned to the system through bleed components 26.Bleed components 26 include a solenoid valve 28 which is operable whenany compressor 10 is activated and a metering device 30 such as acapillary tube or an expansion valve. This circuit permits higherpressure liquid refrigerant from the receiver 14 to be reintroduced tothe suction or low pressure side of the system.

The place of reintroduction of the refrigerant to the suction side isdependent upon several objectives. It is anticipated that compressorapplications may require cooler and cooler refrigerant returned to thecompressor in order to assure motor cooling of hermetic or semi-hermeticunits. Even in open, direct, or belt drive units, cooler returningrefrigerant may be required to resolve design compromises which comefrom refrigerants and refrigerating systems in order to, for example,eliminate the use of some conventional refrigerants. Therefore, in orderto provide cooler return gas, the receiver bleed components through line26 may route refrigerant to the compressor or portion thereof whichrequires such cooling. The amount of cooling available may be regulatedby the adjustment or design of the metering device. In the alternative,a suction line manifold or an accumulator could be utilized, it beingintended that the refrigerant be injected downstream of the expansionvalves.

As will be obvious to those skilled in the art, the place for injectingthe refrigerant will be determined by the demands placed on theindividual system and it is not intended that this invention be limitedto any particular place for injecting.

The ambient compensated pressure regulating valve 18 typically is aconventional design as is its sensor 16. The valve may be a mechanicalvalve utilizing a biased diaphragm or bellows or it may be electronicand the sensors may be electronic. The electronic system would receivesensor information which would then control an electromechanical valvealso of conventional design. Accordingly, this invention is not intendedto be limited to the particular type of ambient compensated pressureregulating valve, or other type of regulating valve utilized.

With reference to FIG. 2, there is shown a system with a differentmethod for expelling excess liquid refrigerant from the receiver tank.During periods of low ambient temperature, the condensing pressurefalls. In this instance, a line 30 is provided from the compressor 10output. Gas through this line is controlled by an ambient compensatedpressure regulating valve 32 which measures the difference in pressurebetween the pressure registered at sensor 16 and the receiver pressureas measured through line 34. At the differential, the output from thecondenser 22 can pass through line 20 and valve 18 into the receiveralong with hot gas under pressure through line 30 in valve 32. Theliquid then reaches the receiver relatively warm and exits the receiverthrough line 36. Valve 38 is a check valve to ensure against a backwardflow of liquid from line 22 into the receiver 14. If necessary, afurther differential pressure valve 40 may be provided which registersthe differential pressure between its sensors in lines 42 and 44 wherebyit functions as a pressure reducing valve to facilitate the flow of hotgas from the compressor through line 30 to the receiver 14.

Therefore, in both embodiments, as shown in FIGS. 1 and 2, the receiveris not normally in the refrigeration cycle and is only used to storerefrigerant not needed in the flow path. Only excess refrigerant isstored in the receiver, thereby reducing the charge to the system. Inaddition, it maximizes liquid subcooling.

The invention may be embodied in other specified forms without departingfrom the spirit or essential characteristics thereto. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which may come within the meaning and rangeof equivalency of the claims are therefore intended to be embracedtherein.

We claim:
 1. In a refrigeration system for circulating refrigerantincluding in series a condenser, an expansion valve, an evaporator, anda compressor in a closed loop, the improvement comprising:a receiver;and first means carried by said system for diverting refrigerant fromsaid loop downstream of said condenser to said receiver only responsiveto the difference between the saturation pressure caused by condenserambient and the internal pressure within said loop downstream of saidcondenser.
 2. The system of claim 1 further comprising:means formetering a flow of refrigerant from said receiver and injecting saidflow into said loop downstream of said metering device.
 3. The system ofclaim 2 wherein said metered flow is injected any place betweenexpansion valve and the place when compression begins within thecompressor.
 4. The system of claim 2 wherein said flow is injected intosaid loop any place that is at a lower pressure than the receiver. 5.The system of claim 1 wherein said receiver has an outlet incommunication with said loop downstream of said means for diverting,said system further comprising:second means in communication with saidloop downstream of said compressor for diverting refrigerant underpressure therefrom to said receiver responsive to a difference betweenthe saturation pressure caused by the condenser ambient and the internalpressure at said receiver; and one way conveying means responsive tosaid second means for conveying refrigerant from said receiver into theloop.
 6. The system of claim 5 wherein said second means includes anambient compensated differential pressure valve.